The assembly mechanisms of algal community across different habitats mediated by sediment in the heavily sediment-laden Yellow River

Suspended sediment particles in river water exert dual effects on algal growth depending on concentration. However, the diversity patterns in riverine algal communities across different habitats are insufficiently explored at different sediment concentrations. To ascertain the environmental factors shaping distinct algal communities, we collected water and sediment samples from 44 sections along the mainstream of the Yellow River, a continent-scale river with heavy sediment loads in China. The community composition and assembly dynamics of free-living, particle-attached, and surfacial-sediment algae were assessed using high-throughput sequencing targeting the V4 region of the 23S ribosomal ribonucleic acid genes. The findings reveal a noteworthy resemblance between the communities of free-living (FL) and particle-attached (PA) algae, while the surfacialsediment (SS) algae community exhibits significant dissimilarities. Sediment concentration emerges as a critical factor influencing the mechanisms of algal community assembly, with homogeneous selection exerting a more prominent influence in habitats rich in sediment. Conversely, the role of dispersal limitation diminishes under such conditions. Moreover, the presence of small-sized suspended sediments enhances the adsorption of algae, resulting in reduced community variability across various habitats. The composition of algal communities is primarily shaped by water quality, with additional indirect influences from elevation and land use. Notably, the high sediment loads in the Yellow River counteract the positive impact of nutrients, thereby imposing limitations on algal growth within this ecosystem.